This invention relates to a fluid compressor, and more particularly to a radial type fluid compressor adapted for use in air conditioning of motor vehicles.
In general, it is desirable that compressors for use in an air conditioner for motor vehicles should be designed compactly in size and should have a high compression efficiency at the same time to permit installation thereof in a limited engine space.
In order to comply with such requirements, a fluid compressor has conventionally been proposed which comprises: a cylinder casing formed therein with vertical and horizontal cylinder bores intersecting with each other in a common plane; two pairs of pistons, each pair being slidably fitted in each of the cylinder bores; an outer shell member fitted on the cylinder casing, the outer shell member and the cylinder casing forming a compressor housing; a drive shaft extending through the casing and the outer shell member, the drive shaft having an eccentric portion formed at a central portion thereof, the eccentric portion being located at the intersection of the cylinder bores; a pair of bearings provided at opposite ends of and near the eccentric portion of the drive shaft; a low pressure chamber formed around a portion of the drive shaft near an end thereof; and a high pressure chamber formed around and adjacent each of the cylinder bores.
With this arrangement, the proposed fluid compressor has a shortened longitudinal size or length and is capable of compressing refrigerant gas at a higher rate.
According to this proposed compressor, since the drive shaft has an eccentric portion located at a center thereof, the upper and lower and left and right pistons received in the vertical and horizontal cylinder bores have to be manufactured separately and coupled together in pairs by means of yoke members.
This compressor therefore requires many component parts and is complicated in structure, making it difficult to put together the same. Further, the above-mentioned arrangement does not permit smooth lubrication of the piston-mounted portions and the drive shaft bearing portions of the compressor, causing difficulties in the sliding motion of the pistons. Still further, since the cylinder bores are each enveloped in a high pressure refrigerant gas, the cylinder housing is difficult to cool and is accordingly apt to be overheated, resulting in a low gas compression efficiency. In addition, it is rather hard to mount the outer shell member onto the cylinder housing in a sealed manner.
To overcome the above-mentioned disadvantages, a compressor has been proposed according to Japanese Patent Application No. 53-63771, assigned to the same assignee of the present application, which comprises: a front part casing formed therein with a drive shaft bearing section and a refrigerant containing section having a refrigerant suction chamber and a refrigerant discharge chamber arranged concentrically with each other; and a cylinder housing secured to a rear end of the front part casing in an abutting manner, the cylinder housing being formed integrally with a vertical cylinder and a horizontal cylinder cruciformly intersecting with each other in a common plane on an outer end surface thereof. A drive shaft is supported in the front part casing in an overhung fashion. That is, it has a rear end thereof formed as an eccentric end which is projected in a central space defined in the cylinder housing. According to this compressor, a pair of double head type piston units are housed in a vertical cylinder and a horizontal cylinder in a fashion crossing each other, wherein these piston units are coupled to the eccentric end of the drive shaft through a box-like sliding member. Lubricating oil in the refrigerant can be introduced into the cylinder housing from the refrigerant suction chamber formed in the front part casing through a through bore formed in the drive shaft and a main bearing supporting the drive shaft. Thus, the compressor is simple in structure and is easy to assemble as well as high in refrigerant gas compression efficiency and lubrication efficiency, succeeding in overcoming the drawbacks in the first-mentioned compressor.
However, according to this compressor, the drive shaft is supported in the front part casing in an overhung fashion with its eccentric end projected in the cylinder housing as mentioned above. Therefore, if the overhung distance, i.e., the distance between the axis of the piston units and the axial center of the main bearing supporting the drive shaft at a portion near the eccentric end thereof is large, the main bearing can be subject to a considerably large force during operation of the compressor, which results not only in reduction in the life of the main bearing but also in shaking or vibration of the drive shaft. Therefore, the above-mentioned distance should preferably be as small as possible.
In this respect, according to the above-stated proposed compressor assigned to the present assignee, a ball bearing is directly mounted on the inner wall of the front part casing as the main bearing. Accordingly, the ball bearing must have a large size, and in actual manufacture, the leftmost position at which it can be located is just a portion near the junction wall between the cylinder housing and the front part casing. That is, the bearing cannot be located at a position closer to the piston units in a fashion lying over the junction wall. Thus, the distance between the main bearing and the eccentric end of the drive shaft or the piston units is inevitably rather large.